1. Field of the Invention
The present invention relates to a recording medium library apparatus and, more particularly, to a magnetic tape library apparatus having an accessor equipped with a bar code reader.
2. Description of the Related Art
Magnetic tape-units are one of diverse kinds of external storage devices for use with computers. The magnetic tape units operate most commonly on what is known as the open reel system using 0.5-inch wide tapes. The chores of manually loading the open reels have been alleviated by widening acceptance of automatic tape loading devices. With these devices, the operator need only set a desired tape reel onto a receptor which then causes the tape to be loaded automatically. Today, operators' burdens are further alleviated by the widespread use of magnetic tape cartridges. A magnetic tape cartridge, accommodating a tape having the same width as that of open reel tapes, allows the tape to be threaded out of the reel within for automatic tape loading.
A plurality of magnetic tape cartridges are entered in the magnetic tape library apparatus. Any one of the cartridges is selected and loaded to a magnetic tape drive unit for data recording and reproduction. The magnetic tape library apparatus comprises a cell unit having a plurality of cells each accommodating a magnetic tape cartridge; a magnetic tape drive unit for recording and reproducing data; and an accessor for automatically switching magnetic tape cartridges between cell unit and magnetic tape drive unit. The magnetic tape library apparatus further comprises a cartridge entry unit for entering magnetic cartridges into the library apparatus, and an automatic cartridge ejection unit for automatically ejecting magnetic tape cartridges from inside the library apparatus.
The accessor transports magnetic tape cartridges through the magnetic tape drive unit, cell unit, cartridge entry unit and automatic cartridge ejection unit. Magnetic tape library apparatuses of this kind are widely used as an external mass storage device for computers. These apparatuses are required to operate unfailingly when unattended.
The cartridge entry unit transports one by one a plurality of cartridges entered by the operator. The accessor receives each cartridge and stores it into the appropriate cell of the cell unit. More specifically, the cartridge entry unit has a bar code reader that reads a bar code off each of the cartridges entered. The bar code data thus read are sent to a host computer via an accessor controller. In turn, the host computer specifies the address of the cell into which the accessor places the applicable cartridge. For writing and reading of data to and from a magnetic tape cartridge, the host computer first designates the address of the cell from which the accessor extracts the cartridge. The extracted cartridge is loaded into the magnetic tape drive unit. After data are written to and/or read from the magnetic tape cartridge, the accessor takes out the cartridge from the magnetic tape drive unit and brings it into the cell whose address is again specified by the host computer.
With prior art magnetic tape library apparatuses, a plurality of cartridges in the cartridge entry unit are separated one by one for delivery to the accessor. The accessor brings each separated cartridge into the appropriate cell. The procedure takes time if there are a large number of cartridges to be accommodated into the cell unit. One proposed solution to this drawback is to provide an opening on the housing close to the cell unit, the opening allowing a large number of cartridges to be entered all at once into the cell unit. One disadvantage of this solution is as follows: because the bar code reader is provided in the cartridge entry unit, each of the numerous cartridges entered into the cells of the cell unit must be extracted one by one by the accessor and brought to the bar code reader that reads a bar code off each cartridge. With its bar code read, each cartridge must be stored again into the applicable cell. In this case, too, it takes time to read the bar code off each of the numerous cartridges entered and to direct them to the cells having the appropriate addresses.